AC sizing, question for the hvac guys

If you have a 20,000 sq foot building with a 20 foot ceiling height how many tons of cooling would you need? And can you convert that into a HP/amps requirement? This is in the state of Michigan.
Hotest temps get to be 95f at the most.

And this is a single story with cement floor.

If I were to guess, and I am not an HVAC guy I will take a shot and say, 30 tons of air, supplied by 2 roof top units 100 amp disconnect on each unit. (how far off am I?)

How many and what kind of lights? Windows, size, direction and shades? How many people? What kind of equipment inside the shop? How air tight?

20 people, no windows, flourecesnt tubes, basic machine tool equipment, 4 mills, 2 lathes, 2 grinders.

basically a machine assembly room with workbenches and cabinets and fab stuff.

homes with a ambient high of 95 degrees and 78 inside with a average insulation value of 6 inches ceiling and 3.5 inches in walls and 3.5 inches in floors take 1 ton (12000 btu) per 600 sq ft. office space generally 1 ton for 300 sq ft. yours if it's insulated will be somewhere between . there is also a heat load for lights and people , lights and machinery at there wattage at 3 btus per and people working at 8000 btus per , people sitting at 400 btus per . hope it helps . go figure.

Gun Guru,
Ball park, approximately 60 tons. Maybe more, maybe less, depending on building construction and the amount of insulation. That will take care of the building envelope. Internal loads (people, electrical motors on your equipment and lighting) are extra. If you have any major exhaust, that"s extra too because you will need make up air. Depending on your building construction you may want to put these on the ground. The smart thing to do is hire a professional contractor to do the load calculations and installation. I doubt you will find an equipment wholesaler who will sell you equipment of this size direct. Approximate contractor cost is about $600-700/ton +/- for Trane or Carrier depending on heat type and amount and whether there is an econmizer or OA damper is required. You will also need 3 phase power for something this size.

My brothers new house is alway HOT, even with
the air conditioning going hard. He"s complained
several times to the installer..who says, "it was
sized correctly for the house" Obviously it
wasn"t. I"d rather have an oversize unit loafing
than an undersize unit working like crazy and not
keeping up
What are your opinions ? ?

Your brother should get an independent person to do the calculations for him amd review the sizing. Having said that, you won't be happy with an oversize unit loafing along either. Unit won't run enough to keep the humidity under control. Most of the time I try to size AC equipment based on the 95% design conditions, when it is really hot it still feels pretty good to come inside where it should be about 20 degF cooler. Other thing to remember is all sizing procedures assume that the unit is allowed to run continuously and "catch up" over night. If you brother likes to turn the AC off at night and open the windows he may be shooting himself in the foot.

To the original question, I would ballpark it at 50-60 tons AC. Again, get a contractor or engineer to look at it. One question they should ask is how large the motors are running the equipment and how often and for what duration they are working (could be a huge impact or negligible depending on the answers).

Other thing that struck me is that fluorescent tubes may not be the most effective light source from 20' ceilings. Consider a "low-bay" type fixture and light source appropriate for whatever work being done.



YMMV,

Kirk